Photochromism is the reversible function of a certain compound that it changes its color swiftly upon exposure to light including ultraviolet light such as sunlight or light from a mercury lamp and returns to its original color when it is put in the dark by stopping its exposure to light and applied for various uses. As photochromic compounds having this property, fulgimide compounds, spirooxazine compounds, chromene compounds, etc. were discovered. Since optical articles having photochromic properties can be obtained by compounding these compounds with plastics, a large number of studies have been made on the compounding of these compounds.
For example, even in the field of spectacle lenses, photochromism is applied. Photochromic spectacle lenses comprising a photochromic compound function as sunglasses whose lenses are quickly colored outdoors where they are irradiated with light including ultraviolet light such as sunlight and as ordinary transparent eyeglasses whose lenses are faded indoors where there is no irradiation, and demand for the photochromic eyeglasses is growing nowadays.
As for photochromic spectacle lenses, plastic lenses are particularly preferred from the viewpoints of lightweight and safety, and photochromic properties are generally provided to the plastic lenses by compounding the above photochromic compounds. There are known a method in which a photochromic compound is dissolved in a monomer which is polymerized to obtain a photochromic lens directly (to be referred to as “kneading method” hereinafter) and a method in which a layer having photochromic properties (to be referred to as “photochromic layer” hereinafter) is formed on the surface of a plastic having no photochromic properties (to be referred to as “lamination method” hereinafter). Various proposals have been made for the techniques of the kneading method (WO01/005854, WO2009/075388, JP-A 2005-239887 and WO2013/002825A1) and the lamination method (WO01/005854, WO03/011967 and WO05/014717).
As for the photochromic compounds and plastic optical articles comprising these compounds and having photochromic properties, the following properties are required from the viewpoint of the photochromic function: (I) the degree of coloration at a visible light range before ultraviolet light is applied (to be referred to as “initial coloration” hereinafter) should be low, (II) the degree of coloration upon exposure to ultraviolet light (to be referred to as “color optical density” hereinafter) should be high, (III) the speed from the stoppage of the application of ultraviolet light to the time when the compound returns to its original state (to be referred to as “fading speed” hereinafter) should be high, (IV) the repeat durability of this reversible function should be high, (V) storage stability should be high, (VI) the compound should be easily molded into an optical article, and (VII) the mechanical strength of an optical article should be high.
With these technologies as a background, photochromic plastic lenses (optical materials) having high color optical density and high fading speed are proposed. The development of photochromic curable compositions comprising a combination of various polymerizable monomers and a photochromic compound (especially a chromene compound) in the kneading method and the lamination method is now under way.
Since the kneading method in particular makes it possible to mass-produce photochromic plastic lenses at a low cost by using a glass mold, it is now the main production method of the photochromic plastic lenses. Therefore, various improvements have been made on the method.
For example, the above four patent documents concerning the kneading method disclose photochromic curable compositions comprising specific (meth)acrylic polymerizable monomers and a chromene compound. By using these photochromic curable compositions, cured products having excellent mechanical strength and photochromic properties (photochromic plastic lenses) can be manufactured.
The above three patent documents concerning the lamination method disclose (1) a method in which a photochromic curable composition is applied to a plastic lens by spin coating to be cured optically (may also be referred to as “coating technique” hereinafter) and (2) a method in which a plastic lens is arranged with a space between it and a mold to fill a photochromic curable composition into the space and cure it (may be referred to as “two-stage polymerization technique” hereinafter). These three patent documents disclose photochromic curable compositions comprising specific (meth)acrylic polymerizable monomers and a chromene compound, which can be advantageously used in the coating technique and the two-stage polymerization technique. When these photochromic curable compositions are used, laminates having excellent photochromic properties (photochromic plastic lenses) can be manufactured by using the above lamination method.
However, due to growing demand for the improved performance of photochromic plastic lenses, a photochromic curable composition from which a higher-performance lens than before can be manufactured in both the kneading method and the lamination method has been desired.
Stated more specifically, a request for the use of a plastic photochromic lens under high-temperature and high-humidity conditions is increasing. According to studies conducted by the inventors of the present invention, it was found that, when photochromic cured products disclosed by WO01/005854 and WO2009/075388 are used repeatedly under high-temperature and high-humidity conditions, an appearance defect such as a crack may be produced. Further, it was revealed that a photochromic cured product disclosed by JP-A 2005-239887 can withstand repeated use under relatively high-temperature and high-humidity conditions but its fading speed is low and accordingly, its photochromic properties must be further improved.
That is, in the prior art, there is no photochromic cured product which highly satisfies the requirements for photochromic properties and properties under high-temperature and high-humidity conditions at the same time, and the development of a photochromic cured product which satisfies both of them has been desired.
Further, a request for the use of photochromic laminates disclosed by the above three patent documents concerning the lamination method under high-temperature and high-humidity conditions is increasing. According to studies conducted by the inventors of the present invention, it was found that, when the photochromic laminate of the prior art is used repeatedly under high-temperature and high-humidity conditions, an appearance defect such as a crack may be produced. Further, it was also found that a photochromic laminate which can withstand repeated use under relatively high-temperature and high-humidity conditions may not obtain sufficiently high surface hardness.
That is, in the prior art, there is no photochromic laminate which highly satisfies the requirements for properties under high-temperature and high-humidity conditions and mechanical properties (especially high surface hardness) while retaining high photochromic properties, and the development of a photochromic laminate which satisfies both of them has been desired.